Apparatus for determining the voltage of a battery



April 3, 1951 s. c. HURLEY, JR 2,547,324

APPARATUS FOR DETERMINING THE VOLTAGE OF A BATTERY Filed NOV. 26, 1945 9 INVENTOR.

Patented Apr. 3, 1951 APPARATUS FOR DETERMINING VOLTAGE OF A BATTERY Samuel C..Hurley, J'ra Danyillje, Ill.; Wilmina In, Hurley, executrix of'said SamuelC. Hurley, Jr., deceased, assigno'r 't'o Wilmina L. Hurley; Damvillc, Ill.

Application November 26, 1945, Serial N 0. 630,899

This: invention relates to an. improved. appa. ratus for amplification and particularly for am: pliiying small voltage and current, changes. It also relates to an apparatus. for determining an electrical characteristic particularlyfrom a 1 Claim. (01. 175-183);

source of direct currentpotential. V V

One'object oi the invention is to provide; an improved, amplifying system for determining or recording a. relatively weak direct current or voltage orweak diflerentials in voltage by means of measuring instruments requiring relatively high current and voltages. It is also an object of. thisinvention; to. use such weak currents and voltages, after amplification for controlling an: otheroperation.

The amplification of very smalldirect current potentials is, a very difiicult problem which herebefore has not been properly solved, The re 'quired measuringequipment and amplifying systems for making such small measurements, .for example the measurement of; .00005. volt necessitates a device relatively insensitive to eX- ternal electrical conditions and unafiected by variations in the characteristics; of. the ampliiying tubesand the related, equipment required. In. the measurement ofsmallunidirectional voltagefor operating a measuring instrument. or for the control of regulating; devices, man-y di f.- ficulties have been; encountered, Amplification of small unidirectional; voltageby; means of, a direct current, amplifier has not proved success fulsince slow oscillations of the; amplified volt-.- age have occurred due to irregularities. ofthe amplifier tube characteristic, causing a corre, spo n g slo soillat n. n: the. amp ified. outbut... Also external ele tric l.distu ban es and excitementssuch as t e r prese c f an el ctric ight b lb o t sour eof alt ot: h3g current. potential causes an induced'alterhating; current: effect. which; must be completely or: substan i y avoided hen. d termi ing or. utilizing extremely sm ll voltage. chan es- It; is therefore an object-of. my nvention; to.

provide an apparatus which is stable-, 'accurate and r pr duc ble inits; es a d whi h not affected by external electrical; disturbances; and which minimizes the internal; effec s dlle to. difienent; characteristics; of; amplifying tubes;- and the, associated equipment;

. A .furtherobject or; the invention; is to. trans.- pose: a. unidirectional voltage or current on .11- acteristicinto; a single pulse and then; amplk tying". the single pulse after which. the sins-lo pulse is measured or is used. to. QH1 1Q1i-8I111ll)? mentroractuatine another device.

2 Still another object of the invention is; to pro vide a means for eliminating all induced aiter-. nating current which would seriously affect the accuracy and reproducibility of. the mplifying system if not: eliminated;

Still another. object of the invention isto pros.

vicle an apparatus'for testing the voltage and current characte isti s. of batter es n .v simil items which must. meet r gid: specifica ions and. wherein the tolerance of jthe order oflessthfln.

.00005vo1t,

A o her o ect. of; he. nvention s o provide. an. app ratus for. determining small: c rrent an es or to do or inetno cur ent capaci y ot a b t ry w erei t mpos ible t dirootlr check the current. due. to the internal' resistance of the battery which causes a. variation depen n upon the. amount of; curren drawn from the battery- In. my appara us. I a o'o pl s bject. by. draw n a cu r t from t e battery through a standard; or known resistance which reducesthe voltageiand increases the current to approximately a constant value and this constant value can. then. be. measured and. th actual value. can. be correlated with the reduced value of; voltage or; increased. valueoi current by the use of ohms law to, determine the acuseful for. determining Small voltage changesof the order of .00005, volt. It. isuse ul. for (18-: termining the valueof a. resistance. Itis useiful in recording. pyrometry for measuring the volt tage. changes; of thermocouples,v photoelectric cells or radiant energy. changes. It also has. greatutility for determining variations. of electrolytic conditions of industrial solutionspartic ularity; in the determination of pH values. of solutions; wherein. it. is desirable to mea ure ac; curately and automatically: small voltage varis ations. My device, is also; suitable tor measur .in urrent by apply n an: IR drop to thecir cuit, to be measured which. always gives a re: producible result, It is also useful for means of indicating, mechanical stress due to..- an electrif trical change. It is. alsouseful in colorimetry. whi d p s m. slight di o n es oi.v the amount of li ht. rec v d; by; pho o It checking; batteri and the l ke also useful in usetuli in. detain posing the output from the amplifier into a single pulse by means of a capacitance coupling to a control grid of an amplifying tube and then amplifying the single pulse.

Other objects, advantages and uses will become I apparent b referring to the drawings in which Figure 1 illustrates a complete wiring diagram and amplification system for comparing a battery for its voltage characteristic with a standard battery of known voltage characteristics;

Figure 2 is a modification of the diagram shown in Figure 1 for measuring small current differentials or for measuring the current capacity of a battery by drawing current from the unknown battery through a resistance of known Value and then amplifying the resulting reduced voltage in the same manner as in Figure 1.

Figure 3 illustrates another modification of Figure 1 for determining resistance characteristics.

,Figure 4 also shows another means for determining resistance characteristics employing the amplifying system of Figure 1.

. Figure 5 shows the use of a circuit breaker switch for-determining voltage and current characteristics in pyrometer measurements and the like where the connection must be frequently broken in order that anotherpulse may be amplified by the system of Figure 1..

V, Figure 6 shows a graph of the current and voltage changes when the current is drawn through a resistance as shown in Figure 2 and is particularly useful inchecking batteries.

Figure 7 shows an apparatus for comparing the amount of light received by the photoelectric cells. I

Figure 8 shows amount of light received by a photoelectric cell. Both Figures 7 and 8 employ the amplification system shown in Figure 1.

Figure 9 shows the position of an indicator for directly. indicating the current and voltage rather thanusing currents or. voltages or resistances as acontrol means such as shown in Figure 1.

. Figure 1 illustrates a method and apparatus for determining whether the voltageof an unknown battery equals or exceeds the voltage of a standard or known battery. The amplification system shown in Figure 1 however has a wide variety of uses as heretofore discussed. However for the sake of illustration of the amplification circuit, it will be described in connection with the determination of a voltage characteristic of a battery. b An unknown battery I is to be compared with a known battery 2 and if the battery I does not equal or exceed the voltage of battery 2, the apparatus ofFigure 1'-will reject the battery I. The battery I is placed in an inspection zone not illustrated or described since it forms no part of my invention. The positive side of the battery is grounded at 3. The negative side is connected to the control grid 4 through a known resistance 5. The negative side of battery I is connected to the control grid 4 for reasons which will be hereinafter explainedf The positive side of-batteryZ-is also connected to ground at point 6 and the negative side is also connected to the control grid 4 through-a known or standard resistance '1. The amplifying tube 8 is a standard triode type vacuum tube. The cathode 9 of tube 8 is connected through resistance In to ground at II in order to obtain a normal bias on the tube such that the tube is conducting in approximately the middle of its operating characteristic. It is apparent that if the voltage .of battery l equals or exceeds the voltage of battery 2, less current will flow through the tube 8 due to impressing a higher negative bias on control grid 4. If the battery I is of less voltage than battery 2, a more positive bias will be placed on the control grid 4 causing more current to fiow through tube 8.

The cathode 9 is connected from point IE to point I3 through the condenser IS. The capacitance coupling of the cathode to the control grid obtain regeneration which increases the sensitivity of the amplification system. However the capacity of the condenser must be sufiiciently low in comparison for the value of the resistance [0 in order to avoid self-sustained oscillation. As much regeneration as possible is desirable and therefore the value of the condenser l5 in comparison with the resistor If! is only lowered to a point to avoid self-sustained oscillation. It is obvious that if such oscillation were obtained it would be impossible to obtain only a single pulse. In using a s-andard vacuum tube of the triode type, such as tube 8 which is commonly referred to as the high gain type, the condenser i5 is of the order of .01 microfarad and the resistance In is approximately 400 ohms. With these values of the condenser l5 and resistance It}, substana means for determining the tial regeneration is obtained and yet self-sustained oscillations are prevented.

The anode circuit of tube 8 contains a load resistor l8 connected to a positive source of direct current potential at ll. The cathode is connected through resistor l8 from points 12 to [1 in order to ob.ain a constant voltage on the cathode.

A control grid [8 in asimilar triode tube 20 is connected to point 2| through the condenser '22. The tubes 8 and 20 are out of phase. The

I use of the condenser 22 transpose the output C a ge of the tube 8 into a single pulse and the control grid [9 receives the single pulse. The obtaining of a single pulse is advantageous because direct coupled amplification is unsuitable, unstable and is affected by minute changes in voltage and the single pulse feature of my invention is stable and not subject to minute changes in voltage. The control grid i9 is connected to the ground 23 through the resistor 24 .3 as part of the biasing means for tube 20. Point 25 below resistor 24 is connected to point 26 or to the control grid l9 through the condenser 21. As heretofore pointed out, great care must be taken to' substantially eliminate all induced alternating current from exterior sources and the condenser 21 bypasses any induced alternating current from external sources to the ground 23 and therefore the accuracy or results of my amplifying system is not affected.

The cathode 28 of tube 20 is connected to the ground 29 through the resistor 30 and is also connected through the resistor 3i to a direct current positive source of potential at 32 in order to again provide a constant voltage on the cath ode. The anode circuit'contains the load resister 33 connected to point 32. No bypass for induced alternating current is provided in this stage of amplification since it has been found that it is not necessary.

The control grid34 of a thirdtriodeivacuum is- 180-* out of phase with the tube 35.

eeer type tube is connected through condenser 36 point 31 and thus-tube 35 is 180 out of phase with tube 20; The control grid 34 is connected to; ground at- 3 1 through the resistor 38-.

The cathode of tube 34 is connected through a typical choke coil 39 to the ground 40'. The choke con i's'pro'vid'ed for the elimination of the effect of any exteriorly induced alternating current since the choke coil induces an alternating cur rent opposite and equal toany alternating current caused byexternai excitement. The cathodeof tube 34 is connected to ground 4| through voltage dividing resistor 42 and also connectedthrough the resistor 43 to a positive side of a direct current source of potential at 44-. The anode circuit of tube contains'a load resistor 45 and below the load resistor 45 the control grid 46 of e gaseous-filled"arc-discharge typect a'rnpliiiying tubefl is connected at'pei'nt 48. Tube t! The cathode 48 is biased through the dividing resistor 49 and connected topoint. It is also connected to the control grid 46 through condenser 50 which provides a bypass for an exteriorly induced alternating current. The operating source of power for the tube 41 is provided by a suitable source of direct current at points 5! and 52 The screen grid of the tube 47 is connected to the cathode in conventional manner as shown. The anodecircuit of the tube 41' contains a relay coil 53* which when energized actuates the relay switch 54 which in turn controls the control oir- I cuit 55 which isthe means for accepting and rejecting the battery according to whether or.

130 out of phase; when the tube 4'! ionizes, tube 35 is substantially in-cut-off'position, tube 20 sub stant'ially approaches saturation in conductance tube 8 has had its control grid 4 driven in inorenegative direction therebyreducing the flow of'current through, the tube 8 For, a bad battery or when the unknown battery I is of less voltage than battery 2', the control grid 4 is driven in a more positive direction causing more current to flow through the anode circuitof the tube 8 which drives tube 20 to substantial cut-of: position, tube 35 approaches saturation, tube-4'I- does notionize, the relay coil 53 is not activated; the relay switch 54, is not closed; and the control circuit 55 therefore rejects the battery.

one operatiomthe unknown battery is-compared with a known battery of 1.3 volts. Thereiore if theunknown battery I equals 1.3 volts or is gr'eat'er than 1.3 volts, the battery isjgood. If the unknown battery for example should be 1.5 volts as comparedto the; standard battery of 1.3 volts, it is obvious that the control gri'd I is driven in a more negative direction and as herebe'fore explained, battery I would be accepted. true because there is a flow, of current through resistor 5whi'ch impresses a more neg'a' tive bias on the tube 8. If the unknown battery I is of less potential than 1.3, it means in effect that c ntrol grid? is biased more; positively and therefore the bias is changed; in a positivexdiiectionand the tube'8'will conduct more current.

The tubeis normally biased. when no unknown;

batteryis connected to the control grid 4 such thatthe tube is always conducting some current which increases the sensitivity of the amplifica ti'on.

Another important feature is thatthe resistors 5- and I are of different values. In testing a,l.2. voltage battery the resistor 5- has a value. of 250,000 ohms and the resistor! a value 0f750,0'00 ohms. Having resistor 5 smaller in comparison with resistor 7 increases the sensitivity because any slight voltage change in battery I ha an increased efiect over a circuit where the two resistors are equal. Furthermore having the re sister 1 relatively large prevents damage to the control grid 4 in case a dead cell I were placed in inspection position since under those circum--. stances if the resistor I were low, an excessive positive voltage might be impressed on control grid i seriously damaging the grid and the characteristics of the tube. Damage to the control grid 4 is further prevented by having the negative side of the unknown battery I and the known battery 2 connected to the control grid. If the unknown cell l should greatly exceedwhat is to be expected, all that will happen in the circuit shown will be to drive the control grid in-a more negative direction which causes less current to flow through tube 8 and no damage will occur. However if the positive sides of the batteries were connected to the control grid and the voltage valuewas higher than expected a sufiiciently high positive potential might be placed on the con trol' grid i resulting in damage to the charac teristics of the tube. 7

Referring as to how the pulse is obtained, let us assume that the plate circuit of the tube 8 is at rest. In this circumstance there is a constant voltage impressed upon the capacitance coupling condenser 22 and since there is no electronmotion, there is no change in the value of the potential. When the plate circuit of the tube 8 approaches B+ potential or the potential or" the point IT, a positive potential is impressed on one side of the condenser. In order for the condenser topass an impulse or a single pulse, it mustbe connected to ground through the resistor 24 so that the electronsare attracted to the opposite plates of the condenser causing a voltage drop across the resistor 24 which impresses a positive potential on the control grid I9. As the plate circuit of the tube 8 approaches ground poten ti'al, a comparatively negative potential is impressed on the condenser 22 which will repel electrons from the opposite plates. These electrons in order to get away from the plate will pass through the resistor 24 to ground creating a current flow through the resistor 24 which du to the voltage drop impresses a negative potential on the control grid I9. Thus it is seen that only a single pulse is received by the tube 29 and irr'i mediately thereafter the bias on the control grid tends toreach equilibrium or return to its normal bias. A capacitance coupling to the control grid', similar to the capacitance coupling including condenser 22 and resistor 24, could be connected between the point 56 and the control grid 4' and in that case the tube 8 would also only receive a pulse instead of receiving the direct current voltage as long as the battery I is in the test position. However capacitance couplings have a certain amount of voltage drop and the use of a capacitance coupling at the point 56 would greatly reduce the sensitivity and it has been found that in most casesthe diiiiculties 7, previously discussed in amplifying small-direct current voltages are sufficiently overcome by having the capacitance coupling between tubes 3 and 20 and a similar capacitance coupling is not required at point 55. In other words, by my preferred method of amplification, I do not sacrifice reproducibility of results and I gain considerable sensitivity in the circuit. Once a pulse is received by the amplifying system that is all that is received regardless of how long the battery I is in its test position. However, I provide a second capacitance coupling between tubes 20 and 35which ha a primary advantage of avoiding separate circuits for biasing each of the individual amplifiers which makes for a more compact unit and furthermore it increases the sensitivity and tends to make the entire amplification system more stable. There i no capacitance coupling required between tubes 35 and d5.

Since when gas filled arc discharge type tubes like 4'! once ionize, when connected to a source of current potential across points 5i and 52, they continue to ionize and will not return to normal condition until the anode voltage is substantially reduced, a capacitance coupling would have very little effect on the tube 27 and furthermore it would be difiicult to obtain a biasing of the tube sufficiently critical due to the short pulse impressed by a capacitance coupling between the tubes 35 and Al and for that reason a capacitance coupling is undesirable.

Batteries like battery i can be tested at the rate of at least 60 per minute. The time from the time the battery is placed in the inspection position until the relay switch 511 is actuated is about .15 second. The complete cycle is about .75 second. One of the reasons for this rapid inspection is the provision of switch 5'? connected to ground 58 although it could be accomplished by a bypass around the resistor '24 to ground 23 instead of the switch being connected to ground 58. As soon as a pulse has passed through the system, the switch 5? as well a a similar switch 59 connected to ground 60 is closed which bypasses any charge on condensers 22 and 36 to ground rendering the system inoperative. Although the condensers 22 and 36 if not grounded would leak through the resistors 24 and 38 and eventually reach equilibrium and although this is very rapid, it is not as rapid as desirable in high speed inspection operations. Therefore in connection with the inspection of the battery I, switches 52' and 59 are actuated by cams (not illustrated or described) correlated with the inspection operation shortly after the battery i is placed in inspection position between the ground 3 and the resistance 5, in order to quickly place the amplifying system in condition for the next inspection. In addition such grounding prevents undersiable surges through the system. One of the most important advantages is the starting of each inspection from same electrical reference point. By this means it is not necessary to wait between inspections or recordings for the condensers 22 and 35 to leak through their respective resistors to ground.

The switch 6! has a very important function also. When the tube is connected across a source of direct current, once it is ionized, it will continue to conduct until the anode voltage is materially reduced and therefore a voltage lowering switch connected in parallel with resistor 6| must be provided to place the system in condition for 'the next inspection. The switch Si is also actuated'by a cam correlated with the inspection mechanism for battery I and with-the time-cycle for the circuit so that such change of the voltage by the opening of the switch 6! will not occur until after the battery 1 has been tested and has had time, as controlled by the control circuit 55 and. the relay switch 54, to pass to the proper chute into which either good batteries are placed or bad batteries are placed. If this switch were actuated too soon to deionize the tube 41. and place it in condition for the next inspection operation, there would not be suflicient time to permit the battery to pass down the mechanical means for dividing the batteries tested into good and bad. Thus the switch 6| actuatedby a cam properly correlated acts as a time-delay for the circuit. Assuming a cycle of .75 second which is the time of the cycle for the circuit in'Figure 1, and calling .00 second the moment battery I is placed into contact with ground 3 and resistor 5, the switch 59 is closed at about 04 second and the switch 5! closed at about .05 second, and the switch BI is opened at about .64 second. It is preferable to close the switch 59 slightly before 51 in order to prevent any surges passing through the system. By taking proper precautions as I have done in my amplifying system, there is no accumulative surge which might occur and greatly destroy the reproducibility of the results.

Thus I have provided: (1) a four stage amplifying system in which the amplifying tubes are alternately out of phase with capacitance couplings between the first and second tubes and between the second and third tubes; (2) no capacitance coupling between the third and fourth tubes since the fourth tube is directly biased by the output of the third tube; (3) means for preventing damage to the first tube; (4) means for completely ofisetting any exteriorly inducedalternating current without sacrificing sensitivity or reproducibility of results; (5) means for quickly placing the circuit into condition for the next inspection; (6) means for deionizing the tube in the last stage of amplification not only for place ing the circuit in condition for the next inspection but also a new timing means for maintainingthe ionization for a definite period to permit the batteries being tested to be properly sorted; ('7) an extremely sensitive amplifying circuit. For example, voltage changes of .00005 voltage may be amplified to about 200 volts or an ampli: fication of about 2,000,000 times. Around 25 volts is the minimum voltage required for operating relay switches of the type shown at 54. (8) I have also provided regeneration and yet do not obtain self-sustained oscillations which increases the sensitivity of the circuit and yet does not interfere with the reproducibility of results. (9) I provide a correlation between the resistors inserted between the unknown battery and the known battery and the control grid of the first stage of amplification which also increases the sensitivity. I

Referring to Figure 2, a modification in th circuit of Figure 1 up to the control grid 4 of the first amplification stage is shown for checking current characteristics from a direct current source of potential such as a battery. Here again it is suitable for many purposes but is illustrated in connection with comparing a known current in terms of voltage against-an unknown current in terms of voltage. Throughout the drawings the same numeral will be used for comparable parts.

In checking the current of a battery, it is essential to first stabilize the current flow and the gta'in reproducible results.

65., that is if a straight connection were made between 64 and 65, the voltage would be substantially zero and. the current would .be a maximum value. This is not feasible since some voltage control grid 4. Therefore the resistance 62 is correlated with the size of the battery being tested such that the current is increased and the voltage reduced to the point X illustrated in the .schematic graph of Figure 6. In this case the .voltage and current are plotted against time. jthe resistance were such that it was attempted "to check the voltage at any point between the and O on the curve it would be so sensitive and the change would be so rapid that it would be impossible to design the circuit to always ob- Therefore the resistance 62 is of such a value that the current is "reduced to a point where it is substantially constant although true enough the less the value of the resistance the greater the increase in current but further increase for all practical purposes is negligible as shown by the graph of Figure 6. In testing a battery of about 1.3 volts the current passing through the resistance 62 is about 1.1 amperage. The resistor 62 has a value of about one tenth ohm in order to reduce the voltage component of the current at point 64 to approximately X value as shown in Figure 6. After the current is drawn through the resistor 62, the voltage is reduced, for a good battery from about 1.3 volts to .2 volt and current drawn is about 1.1 amperes. The known battery 2 must have a value when correlated with the adjustable resistance B3 of about .2 volt or more in order to meet the predetermined current requirements. In other words, I am now comparing a standard or known battery 2 of .2 volt with an unknown battery which if good must have a voltage at point 64 of .2 vo't or higher. Once this is established the circuit is no different than the circuit in Figure 1 and at this point in the operation the switch '65 is closed and the reduced voltage of the unknown battery is compared with a comparable voltage of the known battery and the biasing efiect n the control grid 4 is identical with that described for Figure 1.

Where no internal resistance is encountered, for example in a battery, the reduction of the voltage through the resistor 62 is not necessary, but the current can be checked directly, in which case the resistor 62 is not used.

Referring to Figure 3 a method is shown for determining resistance and here again I will describe the operation in connection with comparing an unknown resistance with a known resistance although ithas many other uses. Referring to Figure 3 the known resistance is being compared with the unknown resistance 69 and the :"n'iust be left at the point 64' in order to bias the resistance 70 there will be a flow of current through the resistor 10 which will impress a nega tive bias on the control grid 4 which reduces the current flowing through tube 8. If theresistance 59 is less than 10, a positive potential will be placed on the tube 4. By use of suitable relays the resistance can be accepted or rejected or as is the case in all the operations discussed herein,

instead of accepting or rejecting an article, an-

electrical characteristic such as voltage, current and resistance can be measured or checked by employing a suitable meter II as shown in Figure 9 in the anode circuit of the tube 41. Therefore I have shown a direct measurement means for determining the electrical characteristic.

Referring to Figure 41, another modification-is shown for determining an unknown resistance which. has a somewhat higher sensitivity than that shown in Figure 3. In the case of Figured the standard resistances and 13 of known. value are provided and the unknown resistance is 12.

By connecting a known resistance 13 in parallel with unknown resistance 12, for a given change in the value of the resistance 12 a greater change is obtained on the bias for the control grid .4 than that obtained in Figure 3. r

series circuit is connected across a known direct a Referring to Figure 5., means are provided .for determining the potential in a temperature measurement or a measurement for pH value where the circuit is always connected to the source of direct current potential. In this case I am not making a comparison of a known and unknown value but I am actually determining the potential and use therefore a recording meter. The recording meter H is positioned in the anode circuit of tube 41 as shown in Figure 9. However since my circuit will only pass one pulse this cannot be done continuously and I therefore must provide a switch 11 to break the connection between the direct current source of potential (indicated by 16) and the control grid 4. Previously I mentioned that the cycle for the circuit of Figure 1 was about .75 second. Therefore the switch l7 may be opened at every .75 second which means that with using the recording meter "H in Figure 9. a reading is obtained once in every .75 second. Therefore I have provided a recording means for indicating temperature, pH value, etc., which depend on small voltage changes as well as means for indicating these voltage changes in a time interval of at least once in every second which is for all practical purposes continuous. At the same time I provide a circuit for obtaining high accuracy since voltage changes of less than .0001 volt can be recorded.

Referring to Figure 7, a means is shown for testing and comparing the output of one photocell against another. Referring to Figure 7 a constant and known source of direct current potential is provided having its positive terminal at 8 and its negative terminal at 19. The circuit for Figure 7 may be used for example in colorimetry measurements where the tube 8| receives the standard amount of light and the tube 80 an unknown amount of light and both must receive the same amount of light to fulfill certain conditions. The control grid 4 is biased by the amount of light which is received by tubes 80 and 8| and slight changes in the amount of light received are accurately reflected by my method" and apparatus.

It is to be kept in mind that in Figure 1 the .relay switch 54 as illustrated is only actuated when the relay coil 53 is actuated but in the various modifications shown this could readily be c hanged jwithin the scope of my invention. In other words, an article could be accepted when the relay switch 53 is not actuated and rejected when it is actuated.

Referring to Figure 8 theoutput of a phototube depending upon the amount of light received can be accurately determined and recorded by fixing and establishing the value of the resistor 83 which will bias the control grid 4 in a predetermined manner and it can be either utilized for controlling another operation or the output can be directly measured by a meter H as shown in Figure 9.

A switch, similar to switch 11 of Figure 5, may

be used in connection with Figures 2, 7 and 8 for the same purpose as described in connection with Figure 5.

The above various descriptions and drawings are not intended to unduly limit my invention but are given only as illustration and my inven-' said common connector, a condenser having connections with said common connector such as to be charged with the voltage at the point of the common connector, an amplifying tube having an anode circuit, a cathode circuit and a control grid, means for biasing said control grid with said charge thereby providing a pulse on said tube, a second amplifier for amplifying said pulse, means for indicating the amplifying pulse, and means including a switch for grounding said condenser to remove the charge after said indication.

SAMUEL C. HURLEY, JR.

REFERENCES CITED The following references are of record in the file of this patent:

V UNITED STATES PATENTS Number Name Date 2,049,306 Matson July 28, 1936 2,086,965 Shepard July 13, 1937 2,137,413 Plaistowe Nov. 22, 1938 2,161,495 Witte June 6, 1939 2,211,718 Freeman Aug. 13, 1940 2,225,231 Pugh Dec. 17, 1940 2,285,482 Wunsch June 9, 1942 2,319,139 Koch May 11, 1943 2,350,545 Bradford June 6, 1944 2,400,245 Mayne May 14, 1946 2,423,671 Wolff July 8, 1947 

